Tension controller



Dec. 23, 1969 x.. H. BUSKER TENSION CONTROLLER Filed Deo'. 11, 1967 I N VEN TOR.

efQgHw/@f W, VW ATTORNEYS United States Patent i Office 3,485,427 Patented Dec. 23, 1969 3,485,427 TENSION CONTROLLER Leroy H. Busker, Rockton, Ill., assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Dec. 11, 1967, Ser. No. 689,509 Int. Cl. B65h 25/18 U.S. Cl. 226-25 19 Claims ABSTRACT OF THE DISCLOSURE A pure iiuidic controller which is capable of adjusting tension on a material and which uses liuid apparatus 1n the control system to accurately control the tension.

Background of the invention This invention relates in general to control apparatus and in particular to a pure fluidic tension controller that might be used, for example, in a paper coating machine.

ln paper coating machines it is necessary to maintain constant and accurate tension on the paper passing through the machine so that the machine does not tear the papernor allow the paper to build up and become entangled and more importantly to present constant conditions for other processes being carried out on the material. The present invention discloses a tension controller which maintains a desired tension very accurately with a minimum of oscillation and pulsation around the setpoint.

It is an object of the present invention, therefore, to provide a novel fluidic tension control apparatus.

Another object of this invention is to provide an improved control system capable of maintaining the function within preset limits.

A further object of the invention is to provide a iluidic tension apparatus which maintains tension constant without regard to the speed of the machine and other variable factors.

A feature of this invention is found in the provision for a sensing device in engagement with a material in which it is desired to maintain a preset tension in operative association with a iluidic pressure system so that variations in tension from the preset valve are corrected. The control system includes an indicator and a plurality of amplifiers and bistable uidic devices to control a tension adjusting means.

Further objects, features and advantages of this invention will become apparent from the following description and claims when read in view of the drawing in which the iigure is a block diagram of the iiuidic tension controller of this invention.

Description of the preferred embodiments The figure illustrates a first pair of rollers and 11 through which a paper mat 12 extends. The paper also extends between a second pair of rollers 13 and 14. The rollers 13 and 14 are mounted on suitable supporting shafts 15 and 16, respectively, which carry gears 17 and 18 that mesh together. The shaft 15 also carries a brake drum 19 which is in operative association with a brake shoe 21. The brake shoe 21 is connected to a brake piston 24. The piston 24 is received within a cylinder 25. A pressure line 77 is connected to the cylinder 25 to move the piston 24 and thus control the brake shoe 21 and the tension on the paper. A motor 27 is connected to drive the rollers 10 and 11. It should be realized that the brake shoe 21 and piston 24 and associated cylinder 25 are illustrated schematically to indicate that the pressure in line 77 is able to control the speed of the rollers 13 and 14 relative to the rollers 10 and 11 to thus adjust the tension on the paper 12.

A tension detector 28 such as a spring mounted roll is mounted along with guide rolls 29 and 30 and supports a fiapper 31 which is in operative association with a nozzle tension detector designed generally as 32. The tension detector 32 is connected to a supply of fiuid 33, as for example, air, which enters the tension detector 32 and emits from the nozzle end 34. The apper gate device 31 causes the pressure within the nozzle device 32 to vary depending upon the proximity of the liapper to the nozzle 34. This back pressure is detected and supplied through a uidic line 36 to a proportional amplilier designated generally at 37. The proportional amplilier 37 may be a liuidic device as, for example, available from Fluidonics, which is a division of the Imperial Eastman Corporation of Chicago, lll. Amplifier 37 receives an input from iiuidic supply 33. A first input port 35 of the proportional amplifier 37 is connected to the line 36. A second input port 38 is connected to a pressure regulator 39. The pressure regulator 39 is connected to a pneumatic or fluid source 40 and carries a knob 41 which adjusts the output pressure from the regulator 39 to `be controlled, as desired.

The regulator 39 may be adjusted by the knob 41 so as to produce a zero output from the proportional amplifier 37 when the tension in the paper 12 is zero. A tension indicator 42 carries an indicator needle 43 and is connected to the output port 44 of the proportional arnplier 37. The other output port 45 of the amplifier 37 is vented to exhaust.

A second proportional amplifier 46? also receives, at its first input port 9 an output through conduit 36 from the tension sensor 32. A fluidic supply 33 is connected to the amplifier 46. The second input port 47 is connected to a regulator 48 which is connected to a fluid source 49. The regulator 48 may be set to any preset pressure by a knob 50.

A pair of outputs 51 and 52 are connected to the proportional amplifier I46 and are respectively connected to the imports 7 and 8 of a third proportional amplifier 53. The iluidic supply 33 is also connected to the amplier 53. A bistable fiuidic device 54 has a pair of input terminals 55 and 56 connected respectively to the outputs 5 and 6 of the proportional amplifier 53. The bistable fluidic device 54 may be a type also obtainable from Fluidonics, a division of Imperial Eastman.

Such devices operate on a single supply and have two control inputs and two outputs. Without an input, flow from the supply will be out either of two outputs. This liow in a stable condition, will continue to liow out of that output until pressure is supplied to the input on the side of the device corresponding to the output. Output flow of the device will then switch to the opposite leg and remain directed out that leg until a pressure is introduced to the input on that side of the device. Flow will then switch to the other output.

The liuidic outputs from bistable device 54 are supplied to lines 57 and 58 which are connected to And gates 59 and 60. The other ports 61 and 62, respectively, of the And gates 59 and 60 are connected together and to a common conduit 63. And gates 59 and 60 are available from Fluidonics or Corning Glass.

The conduit 63 is connected to the output 87 of a bistable fluidic device 64. The bistable liuidic device 64 receives an input from a liuidic supply 33 and has its second output 65 exhausted to atmosphere. The And gates 59 and normally have the full iiuid flow directed to exhaust ports 66 and 67 unless inputs from bistable devices 54 and 64 are both present at the same time or simultaneously. If an output of the bistable device 54 exists on conduit 57, the And gate 59 `will be switched to the output conduit 68. On the other hand, when the output of the bistable device 54 occurs on conduit 58, the output of the And gate 60 will be switched to the output conduit 69. Conduits 68 and 69 are connected to valves 70 and 71, respectively. These valves may be three-way valves capable of operating at speeds as high as 80` cycles per second. Such valves are available from the Fluidic Division of Northeast Engineering, Inc., Hamden, Conn. The valves 70 and 71 have first input ports connected to conduits `68 and 69 and have ports connected to a common conduit 72 which is connected to a brake cylinder by conduit 77. A third port 74 of valve 71 is vented to exhaust. The input ports 75 of valve 70 is connected to a high pressure uid supply 76. The conditions of valves 70 and 71 control pressure in the brake cylinder 25 and thus adjust the tension on the paper.

A bistable device 78 which receives an input from iluidic supply 33 has a first output 79 connected through a volume container `80 and a restriction 101 to one of its input ports 81. The second output port 82 of the bistable device 78 is connected through volume container 83 and a restriction 102 to input port 84. Connection of a bistable device in this configuration creates an oscillatory condition where frequency of oscillation is determined by volumes 80 and 83 and restrictions 101 and 102. The output 82 is also connected through conduit 85 to input port 100 of bistable device 64. The second input port 88 of bistable element 86 is connected through a volume container 89 and a restriction 103 to conduit 63. A pulse appears on conduit 63 having the same frequency as oscillator 78 and has a large on to off ratio.

The structure so far described is capable of sensing high or low tension and provides an on-off or pulse control for the input and exhaust valves which control cylinder pressure and tension. A ymore effective controller can be made if the on-off period or pulse width output of amplifierv 64 can be modulated in accordance -with the amount of error that exists between the tension and the set-point.

To accomplish this, three additional proportional amplifiers 92, V93 and 94 are utilized. These all receive inputs from the fluidic source 33. The differential pressure output from amplifier 46 is fed by conduit 95 to the input port 104 of amplifier 93. The differential pressure from amplifier 46 appearing at output 52 is supplied through conduit 96 to an input port 106 of amplifier 92. A regulator valve 97 is connected to the fuidic supply 33 and includes a reference setting knob 98 to control an output on conduit 99 which is supplied to second input ports 107 and 108 of the amplifiers 92 and 93. Output ports 111 and 112 of the amplifiers 92 and 93 are vented to air, and the second output ports 113 and 114 are connected together and to the input port 116 of amplifier 94. The second input terminal 116 of the amplifier 94 is connected to a regulating valve 117 which is also connected to the fiuidic supply 33, and which has as an adjusting knob 118. A first output port 119 of the amplifier 94 is exhausted to air, and a second output 121 is connected through restriction 122 to volume chamber 89. The restriction 122 mounted in conduit 91 may be controlled by a knob 123 to adjust its size. This controls the flow into the volume chamber 89 of amplifier `64 which in turn shortens the width of the output pulses from the amplifier 64. This in turn controls the valves 70 and 71 through devices 59 and `60 so that they are only open for a very short period of time. When the deviation between the tension and set-point is large the output of the amplifier 94 is diverted to exhaust. In turn, the pulses developed by amplifier 64 become wider (or longer in time) and this in turn results in more on time for valves 70 and 71 for each pulse.

In operation, knob `41 of regulator 39 is adjusted until indicator 42 indicates zero tension when the tension in the paper 12 is zero and the indicator is calibrated so that it indicates the 'tension in the paper.

Knob 50 of regulator 48 is adjusted to set the output pressure of the regulator to correspond to the desired tension in the paper.

Knob 98 on regulator 97 is adjusted to provide an output pressure somewhat higher than the balanced differential pressure from amplifier 46. When the tension signal is nearly equal to the set-point signal, the outputs of amplifiers 92 and 93 will go to exhaust ports 111 and 112. However, if the tension is either high or low then either amplifier 92 or 93 will have its output directed into amplifier 94. Knob 118 is adjusted to control the point of modulation of pulse widths. When the tension and setpoints are nearly equal, amplifier 94 receives no signal from amplifiers 92 or 93 and its output is directed through pulse width control 122 which quickly fills the volume chamber 89 of bistable device 64. This shortens the width of the output pulse of amplifier 64. This in turn controls valves 70 and 71 so that they are opened for a very short period of time.

When the deviation between tension and set-point is large then the output of amplifier 94 is diverted to exhaust. In turn the pulses developed by amplifier 64 become wider or longer in time and this in turn results in more on time for valves 70 and 71 for each pulse.

Ampli-fier 78 receives inputs through feedback restrictive elements 101 and 102 which feed volume chambers and 83. This unit forms a pneumatic oscillator which by adjustment of components could be made to have a pulse output at the rate of about ten cycles per second.

Device 64 is a bistable amplifier connected to give monostable operation. A pulse input on the control port will switch the output from exhaust to the other output port which then feeds back through restriction 103 and volume chamber 89 to switch the unit back to exhaust after a given period of time. The amplifier has only one stable output position and will repeat this function of switching each time an input pulse is received.

Oscillator 78 is used to pulse the monostable device 64 which has an output fed to And gates 59 and 60.

The amplifiers 92, 93 and `94 are used to develop a pulse width modulation of amplifier 64.

In operation, item 32 in the figure, is the tension sensor. This is a nozzle fiapper device in which the flapper is positioned by sheet tension and the nozzle is especially constructed to be capable of operating through a pressure range of 0 to typically 5 p.s.i. The tension signal developed by item 32 is sent to a control port on proportional amplifier 37. The opposing control port has a regulated input to permit the output of the amplifier to be adjusted to zero for zero tension. An indicating gaugeis attached to the output of the proportional amplifier 37 to indicate actual tension.

The tension signal from sensor 32 is also fed to a second proportional amplifier 46 where the tension signal is cornpared to a set-point signal which is adjustable by a pressure regulator. If the tension signal is nearly equal to the set-point signal, the differential output pressure of amplifier 46 will be nearly zero. However, if a large difference Ibetween set-point and tension signal exist, then a large differential pressure will exist at the output of amplifier 46. This differential pressure is fed to a second proportional amplifier 53, for additional amplification and is then fed to a bistable fluidic device 54. Amplifiers 46, 53 and 54 combined form a decision making logic element whose output indicates that tension is either above or below the actual set-point and performs this `function with a minimum of deadband.

The output of amplifier 54 is fed to amplifiers 59 and 60. These amplifiers are termed And gates. In this case, the function is that full flow is directed to exhaust except when the inputs from amplifier 54 and amplifier 64 are both present at the control port. When both control ports of either amplifier 59 or 60 are energized, then they in turn energize valves 70 and 71. Valves 70 and 71 are three-way valves that have an operating speed capability of as high as 80 cycles per second. A typical valve is available from Northeast Engineering, Inc. Activation of valve 70 or 71 will either supply air or exhaust air from the brake chamber 25.

Further logic is introduced to make this an on-off control. Amplifier 78 is a bistable device having feedback through restrictive elements into a volume chamber. This connection forms a pneumatic oscillator which by adjustment of components could be mad to have a pulse output at the rate of say cycles per second. Device 64 is a bistable amplifier connected to give monostable operation. A pulse input on the control port will switch the output from exhaust to the other olutput" port `which then feeds back through a restriction and volume chamber to switch the unit back to exhaust after av given period of time. The amplifier has only one stable output position and will repeat this function of switching each time an input pulse is received. I

Oscillator 178 is used to pulse the Ymonostable device 64 which in turn is fed to And gates 59 and 60; Logic elements thus far assembled provide decision making as to high or low tension and provide an on-off or pulse control of' the input and exhaust vaives. A more effective controller can 'be made if the on-ofiperiod or pulse width output of amplifier 64 can be modulated in accordance with the amount of error that exists between tension and set-point. l

Proportional amplifiers 92, 93 and 94 are used to develop a pulse width modulation of amplifier 64. The differential pressure output of amplifieri46 is fed to amplifier 92 and 93 and compared tota reference pressure which is set to be somewhat higher than the balanced differential pressure. When the tension signal is nearly equal to the set-point signal, the outputv of amplifiers 92 and 93 will go to exhaust. Howeverfifthe tension is either high or low, then either amplifier 92 or 93 will have its output directed into amplifier 94. When the tension and set-point signals are nearly equal, amplifier 84 receives no signal from amplifier 92 or 93 and its"`output then is directed through a width control or restrict-ion which quickly fills the volume cham-ber on amplifier A64. This in turn shortens the width of the output pulse'zlof amplifier 64. This in turn means that valves 70 and 71 are only opened for a very short period of time. Whenlthe deviation between tension and set-point is large then the output of amplifier 94 is diverted to exhaust. In turn the pulse developed by amplifier 64 becomes `widersoijlonger in time and this in turn results in more on timefor valves 70 and 71 for each pulse.

It is seen that this invention provides a fiuidic tension controller using pulse width modulation.

I claim:

1. A fiuidic control system for controlling a condition comprising sensing means sensing the state of the condition, a pneumatic device controlled by the sensing means and producing a fiuid output indicative of the state of the condition, a reference fiuidic source, a proportional fiuidic amplifier receiving inputs from thefreference fiuidic source and the pneumatic device, means for changing the state of the condition being mpn'itored connected to the output of the proportional fiuidicV amplifier, wherein the means for changing the state gf the condition being monitored comprises a 'bistable fiuidic device which receives a pair of outputs from the proportional fiuidic amplifier, a pair of fiuidic And"'"gates connected to a pair of outputs from the bistable fiuidic device, and a pair of control means connected to the fiuidic And gates to control the condition. t

2. In apparatus according to claim 1, wherein the condition being controlled is the tension in a member, a driving means coupled to the member to vary its tension, a brake with a brake cylinder coupled to driving means to adjust its speed and thus vary the tension, a pair of valves connected to the pair of And gates, the valves having first ports connected together and to the brake cylinder, the second port of the first valve open to exhaust, and a source of fluid power connected to the second port of the second valve.

3. In apparatus according to claim 2., a second proportional fiuidic amplifier connected to the output of the first proportional fiuidic amplifier and the bistable fiuidic device receiving the output of the second proportional fiuidic amplifier.

4. In apparatus according to claim 2, a fiuidic oscillator comprising a second bistable fiuidic device with its output ports connected to input ports to form a fiuidic oscillator, and an output from the second bistable fiuidic device connected to the pair of And gates.

5. In apparatus according to claim 4, a pair of volume chambers connected in each connection between the outputs and inputs` of the second bistable fiuidic device.

6. In apparatus according to claim 5 a pair of restrictions connected in each connection between the oiitputs :1nd inputs of the second bistable fiuidic device.

7. In apparatus according to claim 4, a monostable fiuidic amplifier connected between the oscillator and the pair of And` gates.

8. In apparatus according to claim '7, a third volume :hamber connected between the output and the input of the monostable fiuidic amplifier.

l 9. In apparatus according to claim 8, a third restriction mounted between the output and input of the monostable fiuidic amplifier.

10. In apparatus according to claim 9, means for pulse width modulating the output of the monostable fiuidic amplifier. j

11. In apparatus according to claim 10, wherein the means for pulse width modulating the monostable ampli-fier is connected to the outputs of the first proportional fiuidic amplifier and to an input of the monostable fiuidic amplifier.

12. In apparatus according to claim 11, wherein the means for pulse width modulating comprise a third and fourth proportional fiuidic amplifier with first ones of their inputs connected together, the second input of the third proportional amplifier connected to a first output of the first proportional amplifier, the second input of the fourth proportional amplifier connected to a second output of the .first proportional amplifier, a regulator connected to the lfirst inputs of the third and fourth proportional amplifiers, first outputs of the third and fourth proportional amplifiers connected together, second outputs of the third and fourth proportional amplifiers connected to exhaust, a fifth proportional fiuidic amplifier with a first =input connected to the first outputs of the third and fourth proportional amplifiers, a second regulator connected to the second input of the fifth proportional amplifier, a first output of the fifth proportional ampli-fier connected to the monostable fiuidic amplifier.

13. In apparatus according to claim. 12, a restriction in the first output of the fifth proportional amplifier.

14. In apparatus according to claim 13, means `for adjusting the restriction in the first output of the fifth proportional amplifier.

15. In apparatus according to claim I2, wherein a second output of the fifth proportional amplifier is connected to exhaust.

16. In apparatus according to claim 13, wherein the output of the fifth proportional amplifier is connected toI the monostable amplifier between the third volume chamber and the third restriction.

17. A fiuidic control system for controlling a condition with a pulse comprising sensing means sensing the state of the condition, means for changing the state of the condition being monitored, a fiuidic control means connected to said means for changing the state of the condition and receiving an input from said sensing means, and fiuidic pulsing means connected to said fiuidic control means to energize it with a chain of fiuidic pulses.

18. A fiuidic control system according to claim 17 wherein said fiuidic pulsing means includes a fiuidic oscillator. i

7 19. A uidic control system according to claim 18 comprising means for pulse width modulating said fluidic pulsing means receiving an input from said sensing means to produce output pulses which have a width proportional to the deviation of the condition from a reference point. 5

References Cited UNITED STATES PATENTS 2,737,963 3/1956 corrie et a1. 137-85 2,755,032 7/1956 Justus 226-25 10 2,945,637 7/1960 Derrick et a1. 226-25 Aaron et al 226-38 X Foster 226-25 Evans 137-86 Phillips 73-37 Foster et a1. 226-44 Berger et al. 137-86 ALLEN N. KNOWLES, Primary Examiner Us. C1. XR. 

